Question from Craig:
I can't find the on off button or it doesn't appear to be there.

Answer:
It's there, it's just really small. It's in the space directly below the USB connection. Press your whole finger into that space and it'll compress a small button there. Try not to press it with your fingernail as it can damage the button. It's small because a) it's cheap and b) there's limited space. We considered making a better casing for it but honestly it's just too expensive. As a beta unit, we had to decide where to invest and where to say 'good enough'. We tried to invest mainly in the quality of the signal and variety of measurements so there are pieces like this which we didn't do a great job at :\ .